Suyash Bhardwaj Dept. of Computer Science & Engineering Faculty of Engineering & Technology Gurukul Kangri University, Haridwar l1l1 UNIT 1 String Processing

In this Unit l2l2 Structure of string storage: fixed length, variable length, linked list storage. String operations: Indexing,concatenation, length. Applications of string processing: Insertion, deletion, pattern matching, text formation.

Character Strings l3l3 A sequence of characters is often referred to as a character “string”. A string is stored in an array of type char ending with the null character '\0 '.

l A string containing a single character takes up 2 bytes of storage. Character Strings l4l4

l5l5

l6l6

Character vs. String l7l7 A string constant is a sequence of characters enclosed in double quotes. For example, the character string: char s1[2]= " a "; //Takes two bytes of storage. s1: On the other hand, the character, in single quotes: char s2= `a`; //Takes only one byte of storage. s2: a\0 a

Character vs. String l8l8

l #include l int main() l { l char s[1000],i; l printf("Enter a string: "); l scanf("%s",s); l for(i=0; s[i]!='\0'; ++i); l printf("Length of string: %d",i); l return 0; l } Length of string l9l9

#include struct node { int data; struct node* next; }; void push(struct node** head_ref, int new_data) { struct node* new_node = (struct node*) malloc(sizeof(struct node)); new_node->data = new_data; new_node->next = (*head_ref); (*head_ref) = new_node; } int getCount(struct node* head) { int count = 0; // Initialize count struct node* current = head; // Initialize current while (current != NULL) { count++; current = current->next; } return count; } int main() { struct node* head = NULL; push(&head, 1); push(&head, 3); push(&head, 1); push(&head, 2); push(&head, 1); printf("count of nodes is %d", getCount(head)); return 0; } l 10

Example 1 l 11 char message1[12] = "Hello world"; cout << message1 << endl; message1: char message2[12]; cin >> message2; // type "Hello" as input message2:

Example 2: String I/O l 12 String can be input using the extraction operator >>, but one or more white spaces indicates the end of an input string. char A_string[80], E_string[80]; cout << "Enter some words in a string:\n"; cin >> A_string >> E_string; cout << A_string << E_string << “\nEND OF OUTPUT\n"; Output: Enter some words in a string: This is a test. Thisis END OF OUTPUT

getline l 13 The function getline can be used to read an entire line of input into a string variable. The getline function has three parameters: The first specifies the area into which the string is to be read. The second specifies the maximum number of characters, including the string delimiter. The third specifies an optional terminating character. If not included, getline stops at ‘\n’.

Example 3: getline l 14 char A_string[80]; cout << "Enter some words in a string:\n"; //80 is the size of A_string cin.getline(A_string, 80); cout << A_string << “\nEND OF OUTPUT\n"; Output: Enter some words in a string: This is a test. END OF OUTPUT

Example 4: getline Example l 15 char A_string[5], E_string[80]; cout << "Enter some words in a string:\n"; cin >> A_string; cin.getline (E_string, 9) ; cout << A_string << "#" << E_string << “\nEND OF OUTPUT\n"; Output: Enter some words in a string: This is a test. This# is a te END OF OUTPUT

Example 5: getline Example l 16 char lastName[30], firstName[30]; cout :\n"; cin.getline (lastName, sizeof(lastName), ','); cin.getline (firstName, sizeof(firstName)); cout << "Here is the name you typed:\n\t|" << firstName << " " << lastName << "|\n"; Output: Enter a name in the form : Chan,Anson Here is the name you typed: |Anson Chan|

l 17

Ex. 6: String Copy Function in l 18 void strcpy(char dest[], const char src[]); // copies string src into string dest example: char name1[16], name2[16]; strcpy(name1,"Chan Tai Man"); name1: name2: strcpy(name2," "); strcpy(name2,name1); ChanTaiMan\0??? ChanTaiMan

Example 7: strcpy in l 19 #include using namespace std; int main (){ char string_1[6] = "Short";// character strings char string_2[17] = "Have a Nice Day"; char string_3[6] = "Other"; strcpy(string_1, string_2); return 0; }

Ex. 8: String Length Check Function in l 20 // string prototype, already included in string.h //returns length of string(not counting'\0‘) //you don't need to include it in your program int strlen(const char[]); int string_length = strlen("abcde"); //string_length is set to 5.

Ex. 9: String Length Check Function Example l 21 #include using namespace std; int main(){ char string_1[5] = "ABCD", string_2[10]=" "; cout << "String 1 = " << string_1 << endl; cout << "String 2 = " << string_2 << endl; strncpy(string_1,string_2,strlen(string_1)); cout << "After copying, string 1 = " << string_1<<endl; return 0; } //output: String 1 = ABCD String 2 = After copying, string 1 = 1234

Ex. 10: String Length Check Function in l 22 //Copy the value of a string to a string variable #include using namespace std; void string_copy(char target[], const char source[], int target_size); //Before: target_size is the declared size of target. //not including '\0'. //After: The value of target has been set to the string //value in source, provided the declared size of //target is large enough. If target is not large //enough to hold the entire string, a string //equal to the length of target will be stored.

Ex. 10: String Copy and String Length Check l 23 int main( ) //Driver function { char short_string[11]; char long_string[] = "This is rather long."; cout << long_string << "STRING ENDS HERE.\n"; string_copy(short_string, "Hello", 10); cout << short_string << "STRING ENDS HERE.\n"; string_copy(short_string, long_string, 10); cout << short_string << "STRING ENDS HERE.\n"; return 0; }

Ex. 10: String Copy and String Length Check l 24 //Uses string.h: void string_copy(char target[], const char source[], int target_size) { int index; int new_length = strlen(source); if (new_length > (target_size)) new_length = target_size ; for (index = 0; index < new_length; index++) target[index] = source[index]; target[index] = '\0'; }

Ex. 10: String Copy and String Length Check l 25 Output: This is rather long.STRING ENDS HERE. HelloSTRING ENDS HERE. This is raSTRING ENDS HERE.

String Comparison l 26 int strcmp(char s1[], char s2[]); /*compares strings s1 and s2, returns < 0 if s1 < s2 = 0 if s1 == s2 (i.e. strcmp returns false) > 0 if s1 > s2 */ int strncmp(char s1[], char s2[], int limit); /* Same as strcmp except that at most limit characters are compared. */

String Comparison l 27 int comp102_strncmp(char s1[], char s2[], int limit) { for (int i=0; i < limit; i++){ if (s1[i] < s2[i]) return -1; if (s1[i] > s2[i]) return 1; } return 0; }

l 28

Ex. 11: String Comparison Examples l 29 str1 str2return valuereason “AAAA”“ABCD”<0‘A’ <‘B’ “B123”“A089”>0‘B’ > ‘A’ “127”“409” <0‘1’ < ‘4’ “abc888” =0equal string “abc”“abcde”<0str1 is a sub string of str2 “3”“12345”>0‘3’ > ‘1’

Some Common Errors l 30 It is illegal to assign a value to a string variable (except at declaration). char A_string[10]; A_string = "Hello"; // illegal assignment Should use instead strcpy (A_string, "Hello");

Ex. 12: Some Common Errors l 31 The operator == doesn't test two strings for equality. if (string1 == string2) //wrong cout << "Yes!"; // illegal comparison Should use instead if (!strcmp(string1,string2)) cout << "Yes they are same!"; //note that strcmp returns 0 (false) if //the two strings are the same.